A universe of variables

The tranquil sight of a starry night gives little hint of the chaotic and ever-changing behaviour of the stars we see. The study of their behaviour - astrophysics - gives insight into the many different types of stars, their births, lives and deaths, their composition and the nuclear furnaces that make them shine, and how they interact with one another.

Many of these stars change brightness and colour very noticeably, over periods varying from hours to years. With so many of them accessible to small telescopes, binoculars and digital cameras, the opportunity for amateur astronomers to make serious scientific contributions is boundless. Variability provides a powerful tool for building and testing astrophysical theories; and acquiring data on variability is largely in amateur hands. It is far from difficult -- anyone can do it.

How you can do variable star science

Whether you observe a variable star through your eyepiece or use a digital or astronomical CCD/CMOS camera, the method is basically the same - you compare the brightness of the variable with that of other stars in the field. If you are doing it by eye there are techniques for improving reliability of estimation, and if you're using a camera there is software to do it for you. To learn about the techniques, visit the educational resources of the American Association of Variable Star Observers.

UY Scl light curve

Light curve of the eclipsing binary UY Scl, observed by Mark Blackford using an 80mm f6 refractor. This was captured over a single night.

Learning about variable stars

To really appreciate (and get excited about) the stars you may be observing, it's vital to get a grip on the whole field of stellar astronomy - the classification of stars (a fascinating topic) and how variable stars fit into the whole field. John R. Percy’s book ‘Understanding Variable Stars’ is an excellent reference. A highly recommended introduction to variable star types comes from the Australia Telescope National Facility - see Variable Types and links therein. The diagram below is from that webpage and shows how variable stars are classified into groups, class and type. On the ATNF website the diagram is interactive, clicking on any part will link to other pages giving more detail.

Variable classification

Getting involved

For variable star work itself the most comprehensive international organisation is the American Association of Variable Star Observers. It has a huge Variable Star Index of meta data on variable stars including position, variability type, and literature references. Its AAVSO International Database contains observational data on tens of thousands of variables going back over a century. It provides interactive data submission and access resources (you should always upload your observational data to the AID). AAVSO has international observing sections you can join, a huge range of educational materials, and many other resources.

Variable Stars South has a range of observing projects particularly aimed at observation of important variables in the southern stellar hemisphere. You can find out about VSS projects from the Projects Page of this website. You can join any of these, and their leaders will mentor and advise on what to do. It helps so much - and energizes you - to work within a group. Which one you join and what you do will depend partly on your equipment, sky access, and time available. Alternatively strike out on your own, make measurements of well-known stars, and submit to the AAVSO AID.

Go to it, have fun, and add to the science!

Pulsating variables

There are two types of pulsating stars, those where the pulsations are radial and are caused by ionisation and recombination of helium and hydrogen which causes shock waves which in turn move the star’s surface in and out; and non-radial pulsations, usually induced by rotation at high speeds. We are interested mainly in the longer period, radially pulsating objects which are suited to the equipment we can use to observe them—the eye, usually with a telescope and binoculars, CCD and DSLR cameras and now some of our members are turning to spectroscopy due to the development of low cost and dramatically improved detectors and software.


Eruptive variables

Eruptive variable stars show irregular or semi-regular brightness variations caused by material being lost from the star, or in some cases being accreted to it. Despite the name these are not explosive events, those are the cataclysmic variables.


Eclipsing binaries

Extrinsic variables have variations in their brightness, as seen by terrestrial observers, due to some external source. One of the most common reasons for this is the presence of a binary companion star, so that the two together form a binary star. When seen from certain angles, one star may eclipse the other, causing a reduction in brightness. One of the most famous eclipsing binaries is Algol, or Beta Persei (β Per).